Polymeric materials that form an inorganic oxide ceramic upon oxidation, for example by chemical oxidation or by oxygen plasmas, have seen wide application, for example in photoresists for integrated circuit production and as oxygen reactive ion etch barriers. A number of investigators have studied the use of silicon-containing homopolymers as etch resistant layers for such applications (see for example Chou N. J., Tang C. H., Paraszcazk J., Babich E. “Mechanism of Oxygen Plasma Etching of Polydimethylsiloxane Films,” Applied Physics Letters, 46: p. 31 (1985); and Gokan H., Saotome Y., Saigo K., Watanabe F., Ohnishi Y. “Oxygen ion Etching Resistance of Organosilicon Polymers,” In ACS Symposium Series: Polymers for High Technology Electronics and Photonics. in Anaheim, Calif., Turner S. R., Bowden M. J. eds., American Chemical Society, Washington, D.C. (1986)). Such materials that contain at least about 10% wt silicon based on the total weight of the polymer are known to form a thin layer of etch resistant SiOx ceramic when exposed to an oxygen plasma. This oxide layer is responsible for their low etch rate relative to polymers containing only C, H, N, and O atoms. This etch selectivity provides the basis for photoresist schemes involving pattern transfer.
One-, two-, and three dimensional periodicity in block-copolymeric, self-assembled structures is also known (Thomas, et al., “Phase Morphology in Block Copolymer Systems”, Phil. Trans. R. Soc. Lond. A., 348: pp. 149-166). Lamellar, cylindrical, spherical, and ordered bicontinuous double diamond morphologies in block copolymeric systems have been identified (see, for example, Helfand, et al., Developments in Block Copolymers. 1; Goodman, I., Ed.; Applied Science Publishers: London, 1982: vol. 1, pp. 99-126; Herman, et al., Macromolecules, 20, 2940-2942, (1987).
A number of studies on the synthesis of block copolymers including blocks comprising silicon-containing polymer sequences have been reported. In some cases, the block copolymers have been studied for use in photoresists in image transfer processes.
Hartney et al. (a), (“Block Copolymers as Bilevel Resists”, SPIE. 539: p. 90 (1985)) describe siloxane-based copolymers used for bilevel photoresists in image transfer processes. Hartney describes lamellar, spherical, and cylindrical phase-separated morphologies. However, the glass transition temperatures of the siloxane blocks are low (below about 0 degrees C.) allowing the low surface energy siloxane blocks to migrate to the interface of the block copolymer with the air modifying the surface properties of the block copolymer. This migration tends to form a continuous layer of a siloxane polymeric species at the surface which is subsequently exposed to oxygen reactive ion etching. This provides a surface with a high degree of etch resistance (due to SiOx formation) but limits the range of obtainable etched structures. Furthermore, the low glass transition temperature of the siloxane block results in poor dimensional stability of the block copolymer.
Gabor et al. (“Synthesis and Lithographic Characterization of Block Copolymer Resists Consisting of Both Poly(styrene) Blocks and Hydrosiloxane-Modified Poly(diene) Blocks”, Chem. Mater. 6: pp. 927-934 (1994)) describe formation of block copolymers with silicon-containing blocks obtained via post functionalization of poly(diene) blocks with hydrosilanes. The materials thus obtained are block copolymers having a poly(styrene) block and a hydrosiloxane-modified poly(isoprene), or hydrosiloxane-modified poly(butadiene), block which formed lamellar structures with one-dimensional periodicity. The materials were used as an imageable layer in a bilayer resist system. As with the materials described by Hartney et al. (a), the materials produced by Gabor et al. have a low glass transition temperature for the silicon-containing phase before conversion to silicon oxide resulting, in some cases, in poor dimensional stability.
Hirao et al. (“Polymerization of Monomers Containing Functional Silyl Groups. 12. Anionic Polymerization of Styrene Derivatives Para-Substituted With Pentamethyldisilyl (Si—Si), Heptamethyltrisilyl (Si—Si—Si), and Nonamethyltetrasilyl (Si—Si—Si—Si) Groups”, Macromol. Symp. 95: pp. 293-301 (1995)) describes the formation of block copolymers from a variety of oligosilyl-substituted styrenes and styrene. However, the average molecular weights of the block copolymers thus formed were relatively low (<30,000), and the morphologies of the resulting structures were not described.
It is also known that polymers can be degraded by chemical oxidation and exposure to ultraviolet (UV) radiation. The degradation of polymers containing unsaturated double bonds in the backbone by ozone, for example, has been well studied (see for example, Razumovskii S. D. et al. “Degradation of Polymers in Reactive Gases”, European Polymer Journal, 7: pp. 275-285 (1971)).
In addition, Koberstein et al. (U.S. Pat. No. 5,661,092) have recently demonstrated SiOx can be formed in poly(siloxane) oligomers by using a combination of ozone and short wavelength UV light. Koberstein demonstrated that a thin layer of SiOx film was formed on the surface of a poly(siloxane) and fatty acid metal soap film after UV-ozone exposure.
Ozonolysis is a known technique to produce porous structures from block copolymers. Lee et al. (“Polymerization of Monomers Containing Functional Silyl Groups. 7. Porous to Membranes with controlled Microstructures”, Macromolecules, 22: pp. 2602-2606 (1989) and 21: pp. 276-278 (1988)) describe the formation of block copolymer structures comprised of self-assembled block copolymers of poly(isoprene) and poly(4-vinylphenyl)dimethyl-2-propoxysilane. Lamellar as well as spherical/cylindrical morphologies were obtained; however, the amount of silicon in the silicon-containing domains of the structure was rather low (<3 atomic % based on the total number of atoms in the silicon-containing domain). The samples were subsequently immersed on a solution of ozone in dichloromethane. The ozonide which was produced upon reaction of the poly(isoprene) with the ozone was then decomposed with trimethyl phosphite in methanol. The result was a porous structure maintaining the periodic structure of the block copolymer structures from which they were formed.
Mansky et al. (“Monolayer Films of Diblock Copolymer Microdomains For Nanolithographic Applications”, J. Mater. Sci., 30: pp 1987-1992 (1995); and “Nanolithographic Templates From Diblock Copolymer Thin Films”, Appl. Phys. Lett., 68: pp. 2586-2588 (1996)) demonstrated the use of ozonolysis to remove poly(butadiene) (PB) domains from block copolymeric structures formed by self-assembly of polystyrene (PS)-poly(butadiene) (PB) diblock copolymers having periodic structures with cylindrical morphology to form porous structures.
Park et al. (Block Copolymer Lithography: Periodic Arrays of ˜1011 Holes in 1 Square Centimeter,” Science, 276: pp. 1401-4 (1997)) discloses a method for producing periodic arrays of holes and dots in a silicon nitride-coated silicon substrate via lithography utilizing a phase-separated PS-PB block copolymer having three-dimensional periodicity characterized by spherical domains of PB in a PS matrix as a masking layer. The phase separated block copolymer was coated onto the wafers and used as a masking layer for lithography. In some examples, before etching, PB domains were removed by ozonolysis from the block copolymer structure comprising the masking layer. The resulting etched articles displayed a periodic structure that was not substantially similar to the three-dimensional periodic structure of the block copolymer mask, but rather was a two-dimensional cylindrical periodic structure resulting from the shadow cast onto the substrate by the etch resistant domains of the block copolymer mask during the etching process.
Recently, Hashimoto et al. (“Nanoprocessing Based on Bicontinuous Microdomains of Block Copolymers Nanochannels Coated with Metals”. Langmuir, 13: pp. 6869-6872 (1997)) reported the removal by ozonolysis of a diene block from a poly(styrene)-poly(isoprene) block copolymer which forms a Ia3d double gyroid structure, thereby forming porous channels in a polystyrene matrix. They subsequently electroplated the surfaces of the channels to form catalytic membrane reactors for chemical synthesis.
The preceding and other techniques represent, in some cases, significant advances in the areas of lithography and self-assembled polymeric structures. However, there is a need in the art for stable, durable, and multi functional periodic structures capable of forming nanostructured and microstructured porous and relief articles; it is an object of the present invention to provide such structures and articles, and further to provide methods for their fabrication.